Applications known as “search engines” are widely available on computer networks such as intranets and the Internet, including the World Wide Web. Search engines typically enable users to locate desired content, e.g., in web sites, etc. Users indicate key words of interest, and a search engine responds with search results, and may also provide listings from advertisers. For example, pay-per-click (PPC) listings may allow an advertiser to pay a search engine advertising or listing fee only when a user selects, e.g., clicks on, the listing. The position of a PPC listing in a set of search results, e.g., second in a set of five listings, may be determined according to a bid amount, i.e., an amount that an advertiser is willing to pay upon a user selection of the listing.
From the standpoint of being selected by a user, it is generally advantageous for a listing to be placed in a higher position, e.g., first as opposed to fourth in a set of five listings, because users often follow a tendency to select listings that are placed higher. Nonetheless, regardless of where they are placed in a set of search results, some listings may be more or less likely to be selected by a user than other listings. Frequently, advertisers will specify a maximum bid amount, i.e., a maximum amount that the advertiser is willing to pay to have a listing included in a set of search results.
Increasing revenues while treating advertisers fairly remains a challenge for online advertising systems. On the one hand, an online advertising system may wish to maximize revenue and therefore display listings according to the highest maximum bid amounts of advertisers. On the other hand, the online advertiser may not wish to discourage advertisers making lower bid amounts from participating in an online advertising system. Ultimately, it would benefit an online advertising system to order listings in such a way that listings would be likely to be selected by the user.